1. Field of the Invention
The present invention relates to a method for manufacturing an ejection element substrate for ejecting a liquid.
2. Description of the Related Art
The ejection element substrate of an ink jet recording head generally has an ejection orifice for ejecting an ink, an ink supply port for supplying the ink onto the ejection element substrate, and an ink flow channel which is communicated with the ink supply port and the ejection orifice, as the basic structure.
There are several parts that become important points in the manufacture of the ejection element substrate. One of the important points is a point of forming an ink flow channel by using a shape. Another one of the important points is a point of forming an ink supply port of a through-hole by etching a substrate.
The ink supply port needs to secure resistance to ink because of its contact with the ink. Because of this, a method is used which employs a crystal anisotropy etching technique for forming the ink supply port on a silicon substrate having the surface of which the crystal orientation is the (100) face. However, an ink supply port formed by this method has an angle of 54.7° with respect to the plane of the silicon substrate, and accordingly the aperture width of the ink supply port occasionally may inadvantageously be large.
As a method of solving these issues of the ink resistance and the width of the ink supply port, a method has been proposed which includes forming the supply port by using a Deep-RIE method and forming a protection film in the interior of the supply port, as is described in Japanese Patent Application Laid-Open No. 2009-202401.
In addition, as for the ink jet recording head, a means for realizing a small droplet has been proposed in recent years so as to comply with a demand of forming an image of higher quality, and an embodiment in which a filter structure is provided has been proposed as is described in Japanese Patent Application Laid-Open No. 2006-035853.
In the ink supply port having on its inner wall an organic protection film with ink resistance, if the miniaturization of a substrate is aimed at, the side wall of the ink supply port is desirably formed in a vertical direction, as is described in Japanese Patent Application Laid-Open No. 2009-202401. When it is considered that the filter structure is formed in the ink supply port by a patterning technology of photolithography, the ink supply port is to be formed from the back face, from the viewpoint that the ink flow channel is formed by the use of a shape, and the position accuracy of the ink supply port is generally determined on the basis of the back face.
However, the filter structure as illustrated in Japanese Patent Application Laid-Open No. 2006-035853 is formed by a patterning operation to be conducted from the side of the surface and accordingly, the filter structure needs to conform to the ink supply port which is formed on the basis of the back face, and in some cases, it may be difficult to align the positions of the filter structure and ink supply port with high accuracy.
Because of this, in order to form the filter structure with high accuracy, the filter structure is desirably patterned in the same way from the back face so as to conform to the configuration of the ink supply port which is formed from the back face. However, in this case, the filter structure is to be patterned relative to the configuration having a high aspect ratio, and accordingly, in the case of patterning according to the photolithography, a coverage failure may occur because a resist cannot be coated on the side wall part, even if a spray coating method advantageous for a step portion is employed. In addition, the resist tends to easily gather in the bottom part, and accordingly the resist there becomes thicker than a specified film thickness, and a patterning failure may occur in some cases. Furthermore, also in light exposure, focusing is difficult even if unmagnified exposure with a high focal depth is used, so that unnecessary reflection occurs at a step portion and an exposure failure may occur.